- NAME
- SYNOPSIS
- DESCRIPTION
- RETURN VALUES
- CONFORMING TO
- SEE ALSO
- HISTORY

# NAME

DSA_sign, DSA_sign_setup, DSA_verify - DSA signatures

# SYNOPSIS

     #include <openssl/dsa.h>

     int    DSA_sign(int type, const unsigned char *dgst, int len,
                    unsigned char *sigret, unsigned int *siglen, DSA *dsa);

     int    DSA_sign_setup(DSA *dsa, BN_CTX *ctx, BIGNUM **kinvp,
                    BIGNUM **rp);

     int    DSA_verify(int type, const unsigned char *dgst, int len,
                    unsigned char *sigbuf, int siglen, DSA *dsa);

# DESCRIPTION

`DSA_sign()` computes a digital signature on the len byte message digest dgst using the private key dsa and places its ASN.1 DER encoding at sigret. The length of the signature is places in *siglen. sigret must point to DSA_size(dsa) bytes of memory.

`DSA_sign_setup()` may be used to precompute part of the signing operation in case signature generation is time-critical. It expects dsa to contain DSA parameters. It places the precomputed values in newly allocated BIGNUMs at *kinvp and *rp, after freeing the old ones unless *kinvp and *rp are NULL. These values may be passed to `DSA_sign()` in dsa->kinv and dsa->r. ctx is a pre-allocated BN_CTX or NULL. The precomputed values from `DSA_sign_setup()` MUST NOT be used for more than one signature: using the same dsa->kinv and dsa->r pair twice under the same private key on different plaintexts will result in permanently exposing the DSA private key.

`DSA_verify()` verifies that the signature sigbuf of size siglen matches a given message digest dgst of size len. dsa is the signer's public key.

The type parameter is ignored.

The PRNG must be seeded before `DSA_sign()` (or `DSA_sign_setup())` is called.

# RETURN VALUES

`DSA_sign()` and `DSA_sign_setup()` return 1 on success, 0 on error. `DSA_verify()` returns 1 for a valid signature, 0 for an incorrect signature and -1 on error. The error codes can be obtained by ERR_get_error.

# CONFORMING TO

US Federal Information Processing Standard FIPS 186 (Digital Signature Standard, DSS), ANSI X9.30

# SEE ALSO

dsa, ERR_get_error, rand, DSA_do_sign

# HISTORY

`DSA_sign()` and `DSA_verify()` are available in all versions of SSLeay. `DSA_sign_setup()` was added in SSLeay 0.8.